Transport block set segmentation

ABSTRACT

Data of a transport block set is to be transmitted in a wireless communication system. The wireless communication system uses adaptive modulation and coding and has a physical layer hybrid automatic repeat request mechanism. Segmentation information for potential segmentation of the transport block set is provided. The transport block set is transmitted with a first specified modulation and coding scheme. The transport bock set is received and whether the received transport block set is determined to meet a specified quality. When the specified quality is not met, a repeat request is transmitted. The first specified modulation and coding set is changed to a second specified modulation and coding set. In response to the repeat request, the transmit block set is segmented into a plurality of segments supported by the second specified modulation and coding set in accordance with the provided segmentation information. The segments are transmitted and at least two of the segments are transmitted separately. The transmitted segments are received. The segmentation process may be applied more than once for a particular TBS transmission.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/279,365, filed Oct. 24, 2002, which claims the benefit ofU.S. provisional application No. 60/357,198 filed on Feb. 13, 2002, bothof which are incorporated by reference as if fully set forth.

BACKGROUND

This invention generally relates to wireless communication systems. Inparticular, the invention relates to transmission of data in suchsystems where adaptive modulation and coding (AMC) and hybrid automaticrepeat request (H-ARQ) techniques are applied.

In wireless communication systems, such as the third generationpartnership project (3GPP) time division duplex (TDD) or frequencydivision duplex (FDD) communication systems using code division multipleaccess (CDMA) or orthogonal frequency division multiplex (OFDM) systems,AMC is used to optimize the use of air resources.

The modulation and coding schemes (sets) used to transmit data arevaried based on wireless channel conditions. To illustrate, a type ofdata encoding (such as turbo versus convolutional coding), coding rate,spreading factor for CDMA system, modulation type (such as quadraturephase shift keying, M-ary phase shift keying versus M-ary quadratureamplitude modulation), and/or a number of sub-carriers for an OFDMsystem may change. If channel characteristics improve, a lower dataredundancy and/or “less robust” modulation and coding set is used totransfer data. As a result, for a given allocation of radio resources,more user data is transferred resulting in a higher effective data rate.Conversely, if channel characteristics degrade, a higher data redundancyand/or “more robust” modulation and coding set is used, transferringless user data. Using AMC, an optimization between air resourceutilization and quality of service (QOS) can be better maintained.

Data in such systems is received for transfer over the air interface intransmission time intervals (TTIs). Data within a TTI transferred to aparticular user equipment is referred to as a transport block set (TBS).For a particular allocation of air resources, a less robust modulationand coding set allows for larger TBS sizes and a more robust modulationand coding set only allows for smaller TBS sizes. As a result, themodulation and coding set for a given radio resource allocation dictatesthe maximum size of the TBS that can be supported in a given TTI.

In such systems, a hybrid automatic repeat (H-ARQ) request mechanism maybe used to maintain QOS and improve radio resource efficiency. A systemusing H-ARQ is shown in FIG. 1. A transmitter 20 transmits a TBS overthe air interface using a particular modulation and coding set. The TBSis received by a receiver 26. A H-ARQ decoder 30 decodes the receivedTBS. If the quality of the received data is unacceptable, an ARQtransmitter 28 requests a retransmission of the TBS. One approach tocheck the quality of the received TBS is a cyclic redundancy check(CRC). An ARQ receiver 22 receives the request and a retransmission ofthe TBS is made by the transmitter 20. To increase the probability ofsuccessful delivery, retransmissions may apply a more robust modulationand coding set. The H-ARQ decoder 30 combines, the received TBSversions. A requirement for combining is that combined TBS sizes areidentical. If the resulting quality is still insufficient, anotherretransmission is requested. If the resulting quality is sufficient,such that the combined TBS passes the CRC check, the received TBS isreleased for further processing. The H-ARQ mechanism allows for datareceived with unacceptable quality to be retransmitted possibly at amore robust MCS to ensure successful delivery and maintain the desiredQOS.

Another approach is to retransmit the TBS using the old modulation andcoding set. However, if the channel conditions dictate that a morerobust modulation and coding set be used or the initial transmission wasseverally corrupted, the combining of the retransmitted TBSs may neverpass, resulting in a transmission failure.

In a system using both H-ARQ and AMC, a change in modulation and codingset may be determined necessary to achieve successful delivery of arequested TBS retransmission. In this situation, the maximum amount ofphysical data bits allowed within the TTI varies with the modulation andcoding set.

Since only one TBS exists per TTI, the effective user data ratecorresponds to the TBS size applied to each TTI. To achieve maximum datarates the largest TBS size is applied to the least robust modulation andcoding set within the TTI. When wireless channel conditions require morea robust modulation and coding set for successful transmission, such aTBS size can not be supported within the TTI. Therefore, each time amore robust modulation and coding requirement is realized, alloutstanding transmissions in H-ARQ processes with TBS sizes notsupported by this MCS and have not been successfully acknowledged arediscarded.

In current implementations, when a TBS cannot be successfullytransmitted utilizing AMC and H-ARQ mechanisms, recovery is handled bythe radio link control (RLC) protocol (at layer two). Unlike a H-ARQrecovery of failed transmissions, the RLC error detection, data recoveryand buffering of a TBS queued in the transmitter (which may be at thenode-B or user equipment as mentioned below) results in increasedtransport channel block error rates and transmission latency,potentially resulting in a failure to meet QOS requirements.

Accordingly, it is desirable to have alternate approaches to recoverunsuccessful transmissions in such systems to allow for support of highdata rates when AMC and H-ARQ techniques are applied.

SUMMARY

Data of a transport block set is to be transmitted in a wirelesscommunication system. The wireless communication system uses adaptivemodulation and coding and has a hybrid automatic repeat requestmechanism. Segmentation information for potential segmentation of thetransport block set is provided. The transport block set is transmittedwith a first specified modulation and coding scheme. The transport bockset is received and the received transport block set is determined tomeet a specified quality. When the specified quality is not met, arepeat request is transmitted. The first specified modulation and codingset is changed to a second specified modulation and coding set. Inresponse to the repeat request, the transmit block set is segmented intoa plurality of segments supported by the second specific modulation andcoding set in accordance with the provided segmentation information. Thesegments are transmitted and at least two of the segments aretransmitted separately. The transmitted segments are received. Thesegmentation process may be applied more than one for a particular TBStransmission.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is an embodiment of a wireless H-ARQ communication system.

FIG. 2 is an illustration of a segmented TBS.

FIG. 3A is an illustration of a segmented TBS with a control messagesent out-of band.

FIG. 3B is an illustration of a segmented TBS having segmentidentifiers.

FIG. 3C is an illustration of a segmented TBS with segment identifierssent out-of band.

FIG. 4 is an illustration of a segmented TBS having transport sequencenumbers.

FIG. 5 is an embodiment of a segmented TBS wireless communicationsystem.

FIG. 6 is a flow chart of segmenting a TBS.

FIG. 7 is an illustration of segmenting a TBS into three segments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Transport block set segmentation can be used in a variety of wirelesscommunication systems, such as FDD/CDMA, TDD/CDMA and OFDM communicationsystems.

To support high data rates, large TBS sizes are applied to each TTI. Toallow for retransmission of large TBS sizes, at more robust modulationand coding sets to ensure successful delivery, segmentation informationis provided with the TBS transmission. FIG. 2 illustrates a TBS withsegmentation information (SI) in a TTI. The data within the illustratedTBS is segmented into multiple segments, segment 1 to segment N. Eachsegment is sized to have a data size that can be supported by a morerobust modulation and coding set. Segmentation information (SI) ismultiplexed with the TBS data. Although the segmentation information isshown as a header in FIG. 2, the segmentation information may be locatedanywhere within the structure of the TBS transmission (in-band). Thesegmentation information can be used for segmentation of the TBS.

Alternatively, FIG. 3A illustrates using control signaling to sendsegmentation information. The control signal is sent on a separatechannel (out-of-band) from the segment data, segment 1 to segment N,(in-band). The segmentation information indicates the manner that theTBS was segmented for use in reconstructing the original TBS in thereceiver.

FIG. 3B illustrates using a segmentation identifier (SID) as in-bandsegmentation information. Each segment, segment 1 to segment N, has acorresponding segment identifier, SID 1 to SID 2, multiplexed with thatsegment's data (in-band). FIG. 3C illustrates using a SID as out-of-bandsegmentation information.

FIG. 4 illustrates a preferred segmentation identifier for a segmentedTBS. The medium access controller (MAC) assigns a transmission sequencenumber (TSN) to each potential segment. If the TBS is segmented, eachsegment's data is associated with that segment's TSN. As shown in FIG.4, each segment has its own TSN, TSN 1 to TSN N. In a wirelesscommunication system employing H-ARQ, TSNs are assigned to each TBS toallow for sequential processing. Using the TSN as a segment identifierreduces modifications required and minimizes additional complexity ofthe system to accommodate segmentation.

FIG. 5 is a simplified diagram of a transmitter 44 and a receiver 46 forretransmitting a TBS in segments. The transmitter 44 may be located ateither a user equipment or a base station/node-B. The receiver 46 may belocated at either a base station/node-B or a user equipment. In currentsystem implementations, AMC is typically only used in the downlink.Accordingly, the preferred implementation of transport blocksegmentation is for use in the supporting AMC for the downlink. Forother systems using AMC in the uplink, transport block segmentation canbe applied to the uplink.

A transmitter 30 transmits a TBS over the air interface 36. A receiver38 receives the transmitted TBS. A H-ARQ decoder 42 decodes eachreceived TBS. If the TBS fails the quality test, a request forretransmission is made by the ARQ transmitter 40. An ARQ receiver 32receives the request and directs the TBS to be retransmitted. Theretransmitted TBS is combined by the H-ARQ decoder 42 and anotherquality test is performed. Once the TBS passes the quality test, it isreleased for further processing.

An AMC controller 34 is also shown in FIG. 5. If the channel conditionschange, the AMC controller may initiate a change in the modulation andcode set used to transfer data. FIG. 6 is a flow diagram illustratingsuch a change occurring in AMC between H-ARQ retransmissions. Atransmitted TBS fails the quality test and a retransmission isrequested, (step 50). To illustrate using FIG. 7, a TBS is transmittedand the received transmission fails the quality test, as indicated by an“X”. It is determined that a change to a more robust modulation andcoding set is required for successful transmission, (step 52). Since amore robust modulation and coding set is needed, retransmission of thesame size TBS may not be possible. The H-ARQ process is reset and theTBS is segmented using the TBS segmentation device 46, (step 54).Typically, with physical layer segmentation, resetting the H-ARQ processis not necessary for proper operation. Each segment or subset ofsegments of the original TBS is at a size compatible with the newmodulation and coding set. To illustrate using FIG. 7, the original TBSis segmented into three segments, SEG1, SEG2 and SEG3. The segments areretransmitted at the more robust modulation and coding set, (step 56).

Each segment or subset of segments is individually transmitted using thenew modulation and coding set. As illustrated in FIG. 7, SEG1, SEG2 andSEG3 are separately transmitted and received. It is also possibledepending on the choice of modulation and coding that any subset may beseparately transmitted and received (SEG1 & SEG3, or SEG2 &SEG3, etc.).If a transmission of a segment or subset of segments fails, the ARQtransmitter 40 requests a retransmission of that segment or subset ofsegments. The transmission of the segment or subset of segments and theretransmission(s) are combined until the segment or subset of segmentspasses the quality test.

To reduce the added overhead required by the segmentation information,preferably, the transmitter selectively dictates when the segmentationoption is to be utilized. To illustrate, if channel conditions aredegrading or are predicted to degrade, the segmentation option may beutilized. This determination may be based on channel qualitymeasurements, previous transmission success/failure rates for particularmodulation and coding sets, or other criteria. A segmentation controller48, preferably in the transmitter, as shown in FIG. 5, decides whethersegmentation is to be supported. The segmentation controller coordinatesoperation with the MAC to add the segmentation information to the TBS.The segmentation decision may be based on various factors, such as cellloading, added users, number of prior retransmissions and measuredchannel quality. The availability of some of this information (e.g. cellloading and added users) to the transmitter depends on whether thetransmitter is at the node-B or user equipment.

1. A method for transmitting data of a transport block set in a wirelesscommunication system using adaptive modulation and coding and having aphysical layer hybrid automatic repeat request mechanism, the methodcomprising: providing segmentation information for potentialsegmentation of the transport block set; transmitting the transportblock set with a first specified modulation and coding scheme; receivingthe transport block set and determining whether the received transportblock set meets a specified quality; when the first specified quality isnot met, transmitting a repeat request; changing the specifiedmodulation and coding set to a second specified modulation and codingset; in response to the repeat request, segmenting the transmit blockset into a plurality of segments in accordance with the providedsegmentation information; transmitting the segments, at least two of thesegments are transmitted separately; and receiving the transmittedsegments.
 2. The method of claim 1 further comprising performing aquality test on each transmitted segment.
 3. The method of claim 2further comprising if one of the segments fails the quality test, thatsegment is retransmitted.
 4. The method of claim 1 wherein a controlmessage comprises the segmentation information and the control messageis sent separate from the segments.
 5. The method of claim 1 wherein thesegmentation information is a segmentation indicator for each segment.6. The method of claim 1 wherein the segmentation information is atransmission sequence number for each segment.
 7. The method of claim 1wherein the providing segmentation information is only selectivelyprovided.
 8. The method of claim 6 wherein a segmentation decisiondevice determines whether to provide the segmentation information.
 9. Atransmitter for transmitting data of a transport block set usingadaptive modulation and coding and having a physical layer hybridautomatic repeat request mechanism, the transmitter comprising: atransmitter for transmitting the transport block set with a firstspecified modulation and coding scheme and capable of transmittingsegments of the transport block set, at least two of the segments beingtransmitted separately; an automatic repeat request receiver forreceiving a repeat request; an adaptive modulation and coding controllerfor changing the specified modulation and coding set to a secondspecified modulation and coding set; and a segmentation device inresponse to receiving a repeat request and the change to the secondspecified modulation and coding set, for segmenting the transmit blockset into a plurality of segments in accordance with segmentationinformation for transmission by the transmitter.
 10. The transmitter ofclaim 9 wherein the transmitter sends a control message comprising thesegmentation information and the control message is sent separate fromthe segments.
 11. The transmitter of claim 9 wherein the segmentationinformation is a segmentation indicator for each segment.
 12. Thetransmitter of claim 9 wherein the segmentation information is atransmission sequence number for each segment.
 13. The transmitter ofclaim 9 further comprising a segmentation decision device fordetermining whether to support segmentation by requesting segmentationinformation.
 14. A transmitter for transmitting data of a transportblock set using adaptive modulation and coding and having a physicallayer hybrid automatic repeat request mechanism, the transmittercomprising: means for transmitting the transport block set with a firstspecified modulation and coding scheme and capable of transmittingsegments of the transport block set, at least two of the segments beingtransmitted separately; means for receiving a repeat request; means forchanging the specified modulation and coding set to a second specifiedmodulation and coding set; means for receiving a repeat request and thechange to the second specified modulation and coding set; and means forsegmenting the transmit block set into a plurality of segments inaccordance with segmentation information for transmission by thetransmitter.
 15. The transmitter of claim 14 wherein the transmittersends a control message comprising the segmentation information and thecontrol message is sent separate from the segments.
 16. The transmitterclaim 14 wherein the segmentation information is a segmentationindicator for each segment.
 17. The transmitter of claim 14 wherein thesegmentation information is a transmission sequence number for eachsegment.
 18. The transmitter of claim 14 further comprising means fordetermining whether to support segmentation by requesting segmentationinformation.
 19. A user equipment for receiving data of a transportblock set in a wireless communication system using adaptive modulationand coding and having a physical layer hybrid automatic repeat requestmechanism, the user equipment comprising: a receiver for receiving atransport block set and determining whether the received transport blockset meets a specified quality and for receiving segments of thetransport block set in subsequent transmissions, the segmentstransmitted using a different modulation and coding set than thetransport block set and at least two of the segments transmittedseparately; a hybrid automatic repeat request decoder for determiningwhether each received transport block set and segment meets a specifiedquality; and an automatic repeat request transmitter for transmitting arepeat request when the transport block set or segments do not meet thespecified quality.
 20. A user equipment for receiving data of atransport block set in a wireless communication system using adaptivemodulation and coding and having a physical layer hybrid automaticrepeat request mechanism, the user equipment comprising: means forreceiving a transport block set and determining whether the receivedtransport block set meets a specified quality; means for receivingsegments of the transport block set in subsequent transmissions, thesegments transmitted using a different modulation and coding set thanthe transport block set and at least two of the segments transmittedseparately; means for determining whether each received transport blockset and segment meets a specified quality; and means for transmitting arepeat request when the transport block set or segments do not meet thespecified quality.
 21. A method for transmitting data of a transportblock set in a wireless communication system using adaptive modulationand coding and having physical layer hybrid automatic repeat requestmechanism, the method comprising: selectively supporting segmentation ofa transport block set; if supporting segmentation is not selected,transmitting the transport block set using the physical layer hybridautomatic repeat request mechanism; if supporting segmentation isselected: appending segmentation information to the transport block set;and selectively segmenting the transport block set prior to transmissionusing the physical layer hybrid automatic repeat request mechanism usingthe appended segmentation information.
 22. The method of claim 21wherein the selectively supporting is decided based on a cell loading.23. The method of claim 21 wherein the selectively supporting is decidedbased on added users.
 24. The method of claim 21 wherein the selectivelysupporting is decided based on a number of hybrid automatic repeatrequest retransmissions.
 25. The method of claim 21 wherein theselectively supporting is decided based on a measured channel quality.26. A transmitter for transmitting data of a transport block set in awireless communication system using adaptive modulation and coding andhaving physical layer hybrid automatic repeat request mechanism, thetransmitter comprising: a segmentation decision device for determiningwhether segmentation information is needed; if segmentation informationis needed, sending a signal; and a segmentation device for selectivelysegmenting the transport block set prior to transmission using thephysical layer hybrid automatic repeat request mechanism using appendedsegmentation information as requested by the signal.
 27. The transmitterof claim 26 wherein the determining is based on a cell loading.
 28. Thetransmitter of claim 26 wherein the determining is based on added users.29. The transmitter of claim 26 wherein the determining is based on anumber of hybrid automatic repeat request retransmissions.
 30. Thetransmitter of claim 26 wherein the determining is based on a measuredchannel quality.